# SimpleCalc.py
#
# Demonstration of the parsing module, 
# Sample usage
#
#     $ python SimpleCalc.py 
#     Type in the string to be parse or 'quit' to exit the program
#     > g=67.89 + 7/5 
#     69.29
#     > g
#     69.29
#     > h=(6*g+8.8)-g 
#     355.25
#     > h + 1 
#     356.25
#     > 87.89 + 7/5 
#     89.29
#     > ans+10
#     99.29
#     > quit
#     Good bye!
#
# 



# Uncomment the line below for readline support on interactive terminal
# import readline  
from pyparsing import ParseException, Word, alphas, alphanums
import math

# Debugging flag can be set to either "debug_flag=True" or "debug_flag=False"
debug_flag=False

variables = {}

from fourFn import BNF, exprStack, fn, opn
def evaluateStack( s ):
    op = s.pop()
    if op == 'unary -':
        return -evaluateStack( s )
    if op in "+-*/^":
        op2 = evaluateStack( s )
        op1 = evaluateStack( s )
        return opn[op]( op1, op2 )
    elif op == "PI":
        return math.pi # 3.1415926535
    elif op == "E":
        return math.e  # 2.718281828
    elif op in fn:
        return fn[op]( evaluateStack( s ) )
    elif op[0].isalpha():
        if op in variables:
            return variables[op]
        raise Exception("invalid identifier '%s'" % op)
    else:
        return float( op )

arithExpr = BNF()
ident = Word(alphas, alphanums).setName("identifier")
assignment = ident("varname") + '=' + arithExpr
pattern = assignment | arithExpr

if __name__ == '__main__':
  # input_string
  input_string=''
  
  # Display instructions on how to quit the program
  print("Type in the string to be parsed or 'quit' to exit the program")
  input_string = input("> ")
  
  while input_string != 'quit':
    if input_string.lower() == 'debug':
        debug_flag=True
        input_string = input("> ")
        continue

    # Reset to an empty exprStack
    del exprStack[:]
  
    if input_string != '':
      # try parsing the input string
      try:
        L=pattern.parseString( input_string, parseAll=True )
      except ParseException as err:
        L=['Parse Failure',input_string]
      
      # show result of parsing the input string
      if debug_flag: print(input_string, "->", L)
      if len(L)==0 or L[0] != 'Parse Failure':
        if debug_flag: print("exprStack=", exprStack)
  
        # calculate result , store a copy in ans , display the result to user
        try:
          result=evaluateStack(exprStack)
        except Exception as e:
          print(str(e))
        else:
          variables['ans']=result
          print(result)
      
          # Assign result to a variable if required
          if L.varname:
            variables[L.varname] = result
          if debug_flag: print("variables=",variables)
      else:
        print('Parse Failure')
        print(err.line)
        print(" "*(err.column-1) + "^")
        print(err)
  
    # obtain new input string
    input_string = input("> ")
  
  # if user type 'quit' then say goodbye
  print("Good bye!")


